In a digital terrestrial hi-vision broadcast tuner for a vehicle installation, when the tuner suffers in a degraded reception state, which disables the reception of normal twelve-segments broadcasting system (hereafter, abbreviated as “a 12-seg broadcast”), the 12-seg broadcast is automatically switched to the reception scheme of a one-segment broadcasting system (hereafter, abbreviated as “a one-seg broadcast”), which is modulated by a broadcast system immune to the fading phenomena. Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) approach, which is admitted as a Japanese standard for broadcast, based on the enforcement of the provision of the Japanese Radio Law Article 38, by using UHF frequency band, divides one-channel of 6 MHz band into twelve-segments for fixed receptions and one-segment for a portable reception, and consequently achieves broadcast transmissions. In the ISDB-T approach, orthogonal frequency division multiplexing (OFDM) is used as a multiplexing system, and 16-state quadrature amplitude modification (16QAM), 64-state quadrature amplitude modulation (64QAM), quadriphase-shift keying (QPSK) and differential quadriphase-shift keying (DQPSK) are used as modulation systems, respectively. Also, in order to correspond to various broadcasting approaches in future, as transmission parameters, there are mode-I to mode-III, in which OFDM carrier spacing are different.
When watching digital terrestrial broadcasts in moving vehicles, fading changes reception electric fields severely. For this reason, diversity reception is indispensable to digital terrestrial broadcast tuners mounted in vehicles. In particular, in a tuner for 12-seg broadcast reception, a phase synthetic diversity by using digital beamforming (DBF) is used in order to secure a high carrier-to-noise power ratio (CNR). In the phase synthetic diversity with DBF, receivers whose number is equal to the number of antennas are required. Thus, the digital terrestrial broadcast tuners for vehicles are marketed at prices equal to three to four times that of digital terrestrial broadcast tuners for home use. Also, when DBF is mounted in mobile apparatuses such as a note PC and the like, electric power consumption is increased, which results in a problem that a viewable time becomes short.
As variable directional antennas, which require only single reception system, there are a phased array (see patent literature (PTL) 1 and patent literature (NPL) 2), load reflection current control type adaptive antenna (see NPL 2), Electronically Steerable Passive Array Radiator (ESPAR) antenna (see NPL 3) and the like. In those antennas, reception signal of each element cannot be directly observed, which consequently requires the use of blind algorism for weight search. Typically, in many cases, since the blind algorism is long in convergence time, application of the blind algorism to high-speed movements is difficult. Also, trial operations of phase shifters are required in the phased array, and trial operations of variable reactors are required in ESPAR antenna so as to execute the weight search. Because these trial operations correspond to channel changes in reception branches, the application of the blind algorism to the reception in the ISDB-T system causes problems such as loss of symbol synchronization and degrade of BER characteristics.